This invention pertains to the art of wheelchairs and, more particularly, to a wheelchair in which the seat can tilt relative to the frame, i.e., the entire seat moves from an upright to a tilted position, and the weight of the user is repositioned to maintain the center of gravity at a stable location between the ground engaging wheels.
The invention is particularly applicable to a power chair and will be described with reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed in related environments and applications.
Known seating systems for wheelchairs allow the entire seat to pivot about a fixed point. Typically, the seating system is actuated via a linear actuator where the seat portion and seat back pivot or tilt as a unit about the fixed pivot point in response to extension and retraction of the linear actuator. Although adequate for some circumstances, it is desired to maintain the center of gravity of the user at substantially the same location whether in an upright or tilted position. The position of the center of gravity is not addressed with the fixed pivot arrangement of the prior art.
A compact, reliable actuator is also desired to provide for durable, yet repeatable performance. Preferably, the actuator should be mounted at a location that is easily secured to the seat assembly and frame, is accessible to a controller, and does not take up a large amount of space.
One known patent that describes a tilting wheelchair arrangement is shown in U.S. Pat. No. 5,044,647. The '647 patent has a tilt/recline wheelchair with a center of gravity compensation. Particularly, a pair of stanchions are secured to horizontal side members at their junction with a vertical support member. A pair of cam follower pins provided on upper ends of the stanchions cooperate with arcuate slots disposed in cam plates mounted at the joint between the seat back and seat portion. A lower end of the cam plate is secured to a seat support bar slidable along a pair of guide rails. As a linear actuator pulls the seat support bar, the seat then tilts from an upright position to a tilted position, the pin providing for the cammed arcuate movement and center of gravity compensation during the tilting process.
Although the '647 patent does maintain the center of gravity of the user between the front and rear wheels of the wheelchair, the tilt mechanism is relatively large and cumbersome. Thus, a simple, economical, and compact tilt mechanism that compensates for the center of gravity is desired.